The present invention relates generally to orthopaedic implants applied surgically and specifically to a new fluted hip nail primarily intended for use in the repair of fractures of the hip or for use in the stabilization of surgically created fractures in the reconstruction of congenital deformities of the hip principally in children. A single piece fluted hip nail is described including an integral solid nail-plate junction as well as instrumentation for use in the insertion and later removal of the implant.
The principal aim in treatment of patients having intertrochanteric hip fractures, and especially the elderly, is the rapid return in full prefracture activities. Local problems that must be dealt with include proximal femoral instability and deformity as well as pain. Rapid mobilization serves to prevent local skin ulceration, urinary stasis, pneumonia, thromboembolic disease, and other complications arising from long bed confinement.
Accordingly, the treatment of itnertrochanteric fractures has conventionally been accomplished by reduction and internal fixation. Most of the prior art fixation techniques serve to alleviate pain and permit the patient to be ambulatory, although they are not generally weight bearing. In some cases the implants are partially weight bearing during assisted ambulation. The elderly patient in most cases does not have sufficient strength or coordination to protect the hip from excessive stress while walking with the assistance of crutches or the like.
The prior art has attempted to provide fixation of the fracture that is so stable that the patient's full weight may bear on the fractured hip. Typical strong nails for this purpose have been developed by E. P. Holt, Jr. (Journal of Bone and Joint Surgery, 45-A: 687-705, June, 1963) and A. Sarmiento (Journal of Bone and Joint Surgery, 45-A: 706-722 June, 1963). Others have suggested altering the positions of the fracture fragments to improve the mechanical resistance of the bone to the disruptive forces during weight bearing. (Dimon et al., Journal of Bone and Joint Surgery, 49-A: 440-450 April, 1967; and Massey, Journal of Bone and Joint Surgery 46-A: 658-690, April, 1964).
The three most common implants presently being used for such fracture reduction and fixation are the Jewett nail, a telescoping screw device, and the Holt nail. Tests on these devices are to be found in the literature; note Journal of Bone and Joint Surgery; 56-A, 899-907, July, 1974; Acta chir. Scandinav. 117: 427-432, 1959. During these tests the Jewett nail showed bending at the fracture site and continued varus angulation at relatively low load levels. Anatomical reduction using a telescoping screw device maintained the desired neck shaft angle until the screw had completely telescoped. Continued loading then produced bending at the screw plate angle. When a femur fixed with a Holt nail was tested, the load rose rapidly and then dropped off as a result of fracture of the trabeculae in contact with the nail. Further loading resulted in bending of the nail.
The forces acting on the head of an adult femur are quite surprising at first glance. When standing on one leg the force would be 2 and 1/2 times body weight; for walking, five to six times body weight. Hence, for a 60 kg man it will be appreciated that the femoral head would be exposed to forces in the range of 150 to 300 or more kg. With regard to the proximal end of the femur, studies show a capacity before fracture of 500 kg for the elderly and 1000 kg for the young. Any implant designed for use in intertrochanteric fracture treatment must therefore approach these levels. Most of the internal fixation devices which have been tested have a failure strength of only 100 to 200 kg.
Hip nails actually undergo two types of bending under the application of force; one is elastic and the other is a permanent type of deformation. When forces act on a nail below its elastic limit, the nail will bend and then when pressure is removed, it will resume its original configuration with no measurable permanent deformation. If the elastic limit is surpassed, however, a permanent deformation will result.
For a more detailed discussion of implant systems with regard to stress parameters, reference may be made to "Biomechanical Principles of Intramedullary Fixation" Clinical Orthopaedics No. 60, 1968, 13-20.
The unitary one-piece fluted hip nail which is the subject of this invention provides significantly improved bending strength in the fixation of fractures as well as in the stabilization of surgically created fractures in hip reconstructive surgery on children. Additionally, the new nail, by virtue of its fluted design, provides improved torsional stability.
A review of the prior art indicates that present implant devices of this type either severely compromise their fatigue and ultimate strength by the provision of central driving recesses and/or central cannulation to facilitate insertion, or sacrifice stability in order to eliminate the need for driving surfaces.
All known trochanteric implants provided with fins or vanes to provide rotational stability, such as Price, U.S. Pat. No. 2,627,855, employ a central bore for driving which seriously weakens the device both with regard to fatigue life and the ultimate load carrying capacity.
The prior art devices which are devoid of such a central bore for driving and extraction forego the rotationally stabilizing flutes or fins in order to facilitate insertion because such projections require forcible insertion into the bone. Therefore, most of the devices now in use employ a central bore which unfortunately is at the central or high stress portion of the nail and support plate.
It should be further noted that most known implants have a small or sharp frontal area for ease in insertion into the bone, and the few that are blunt lack rotational stability.
With regard to instrumentation, the existing implants such as Collison, U.S. Pat. No. 2,612,159, have smooth surfaces in the areas between the screw holes of plate portions which fit against the upper end of the femur which makes it extremely difficult to clamp this portion to the bone without slipping of the clamping instrumentation which would create surface damage to the plate or which could require the instrumentation to obstruct one or more of the screw holes.